Fig. 1. A group of sporangia, x 15. Fig. 1 _a_. Capillitium and spores, x 300. Fig. 1 _b_. A single spore, x 1200. _Diderma cor-rubrum_ n. s., p. 140. Fig. 2. A group of sporangia, x 15. _Diderma asteroides_ List., p. 143. Fig. 3. Sporangia-spread, x 6. Fig. 3 _a_. Same sporangia still unopened, x 4. _Comatricha laxa_ Rost., Cf. Pl. V., 5 & 5 _a_, p. 184. Fig. 4. Sporangia, x 10. _Diderma lyallii_ (Mass.) Macbr., p. 136. Fig. 5. A group of sporangia, x 10. Fig. 5 _a_. Capillitium and spores, x 200. _Lepidoderma chailletii_ Rost., p. 146. Fig. 6. A group of sporangia, x 15. Fig. 6 _a_. Capillitium and spores, x 150. Fig. 6 _b_. A single spore, x 800. _Didymium anellus_ Morg., p. 117. Fig. 7. A group of sporangia, x 10. _Diderma radiatum_ Linn., p. 141. Fig. 8. A group of sporangia, x 8. _Physarum diderma_ Rost., p. 55. Fig. 9. A group of sporangia, x 10. _Diderma rugosum_ (Rex) Macbr., p. 144. Fig. 10. A group of sporangia, x 10. _Diderma niveum_ (Rost.) Macbr., p. 137. Fig. 11. A group of sporangia, x 10. Fig. 11 _a_. Spore and Capillitium, x 600. _Prototrichia metallica_ (Berk.) Mass., p. 258. Fig. 12. A group of sporangia, x 10. Fig. 12 _a_. Same; capillitium and spores, x 300. Fig. 12 _b_. Tip of a capillitium thread to show spiral markings and end-fraying, x 800. _Comatricha aequalis_ Peck, p. 180. Fig. 13. A group of sporangia, x 5. Fig. 13 _a_. Sporangium tip, capillitium, x 200. Fig. 13 _b_. Spore, x 800. _Physarum compressum_ Alb. & Schw., p. 80. Fig. 14. A group of sporangia to show compressed form, x 10. See also Plate XIX., Fig. 12. [Illustration: PLATE XVIII] EXPLANATION OF PLATE XIX _Dictydium cancellatum_ Batsch, p. 230. Fig. 1. The finest phase, as the form appears in the Mississippi valley, x 15. Fig. 1 _a_. Sporangium of the same seen from below, x 35. Fig. 1 _b_. Sporangium--same--seen from above, x 35. Fig. 1 _c_. Cribraria-like net from the top, x 200. Fig. 2. Vertical section of what is believed the typical European form, x 20. Fig. 3. An ellipsoidal piriform phase--var. _prolatum_, x 15. _Physarum compressum_ Alb. & Schw. form _P. affine_ Rost., p. 80. Fig. 4. A group of sporangia, x 12. Fig. 4 _a_. A single spore, x 600. Fig. 4 _b_. Capillitium, same species, x 300. _Alwisia bombarda_ Berk. & Br., p. 209. Fig. 5. Open sporangia, x 6. Fig. 5 _a_. Sporangium of same enlarged to show capillitium, x 20. _Cribraria dictydiodes_ Cke. & Balf., p. 222. Fig. 6. A group of sporangia, x 6. Fig. 6 _a_. Single sporangium of same--lateral view, x 25. Fig. 6 _b_. Same; base view, x 30. _Cribraria aurantiaca_ Schrad., p. 221. Fig. 7. Single sporangium, x 30. _Cribraria rufa_ (Roth) Rost., p. 220. Fig. 8. Sporangium, x 30. _Cribraria piriformis_ Schrad., p. 224. Fig. 9. Sporangium, x 30. _Cribraria splendens_ (Schrad.) Pers., p. 221. Fig. 10. Sporangium, x 30. _Echinostelium minutum_ DeBy., p. 198. Fig. 11. Several sporangia, x 15.